Journal of Volcanology and Geothermal Research 320 (2016) 100–106

Contents lists available at ScienceDirect

Journal of Volcanology and Geothermal Research

j ourna l homepage: www.e lsev ie r .com/ locate / jvo lgeores

Volcán de Colima dome collapse of July, 2015 and associated pyroclasticdensity currents

Gabriel A. Reyes-Dávila a, Raúl Arámbula-Mendoza a,⁎, Ramón Espinasa-Pereña b, Matthew J. Pankhurst c,Carlos Navarro-Ochoa a, Ivan Savov c, Dulce M. Vargas-Bracamontes d, Abel Cortés-Cortés a,Carlos Gutiérrez-Martínez b, Carlos Valdés-González b, Tonatiuh Domínguez-Reyes a,Miguel González-Amezcua a, Alejandro Martínez-Fierros a, Carlos Ariel Ramírez-Vázquez a,Lucio Cárdenas-González b, Elizabeth Castañeda-Bastida b, Diana M. Vázquez Espinoza de los Monteros b,Amiel Nieto-Torres b, Robin Campion e, Loic Courtois f,g, Peter D. Lee f,g

a Centro Universitario de Estudios e Investigaciones en Vulcanología (CUEIV), Universidad de Colima, Av. Bernal Díaz del Castillo No. 340, Col. Villas San Sebastián, C.P. 28045, Colima,Colima, Mexicob Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No. 665, Col. Pedregal de Santo Domingo, Del. Coyoacán, C.P. 04360, Ciudad de México, Mexicoc School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UKd Cátedras CONACYT at CUEIV, Universidad de Colima, Av. Bernal Díaz del Castillo No. 340, Col. Villas San Sebastián, C.P. 28045, Colima, Colima, Mexicoe Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito Científico, s.n. Coyoacán, C.P. 04510, D.F., Mexicof Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester, M13 9PL, UKg Research Complex at Harwell, Rutherford Appleton Laboratories, Didcot OX11 0FA, UK

⁎ Corresponding author.

http://dx.doi.org/10.1016/j.jvolgeores.2016.04.0150377-0273/© 2016 The Authors. Published by Elsevier B.V

a b s t r a c t

a r t i c l e i n f o

Article history:Received 7 October 2015Received in revised form 8 April 2016Accepted 11 April 2016Available online 16 April 2016

During July 10th–11th 2015, Volcán de Colima, Mexico, underwent its most intense eruptive phase since itsSubplinian–Plinian 1913 AD eruption. Production of scoria coincident with elevated fumarolic activity and SO2

flux indicate a significant switch of upper-conduit dynamics compared with the preceding decades of domebuilding and vulcanian explosions. A marked increase in rockfall events and degassing activity was observedon the 8th and 9th of July. On the 10th at 20:16 h (Local time= UTM− 6 h) a partial collapse of the dome gen-erated a series of pyroclastic density currents (PDCs) that lasted 52 min and reached 9.1 km to the south of thevolcano. The PDCs were mostly channelized by the Montegrande and San Antonio ravines, and produced a depositwith an estimated volume of 2.4 × 106m3. Nearly 16 h after the first collapse, a second and larger collapse occurredwhich lasted 1 h 47min. This second collapse produced a series of PDCs along the same ravines, reaching a distanceof 10.3 km. The total volume calculated for the PDCs of the second event is 8.0 × 106m3. Including associated ashfalldeposits, the two episodes produced a total of 14.2 × 106 m3 of fragmentary material. The collapses formed anamphitheater-shaped crater open towards the south. We propose that the dome collapse was triggered by arrivalof gas-rich magma to the upper conduit, which then boiled-over and sustained the PDCs. A juvenile scoria sampleselected from the second partial dome collapse contains hornblende, yet at an order of magnitude less abundant(0.2%) than that of 1913, and exhibits reaction rims, whereas the 1913 hornblende is unreacted. At present thereis no compelling petrologic evidence for imminent end-cycle activity observed at Volcán de Colima.

© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license(http://creativecommons.org/licenses/by/4.0/).

Keywords:MonitoringVolcán de ColimaPetrologyLava dome collapseBoiling-overPyroclastic density currents

1. Introduction

The andesitic stratovolcano Volcán de Colima in western México(19.51N, 103.62W, height 3860 m) is one of the most active volcanoesin North America and is currently in a highly active phase. There havebeen at least 29 significant eruptions since 1560AD, according to histor-ical accounts. Patternswithin this activity are able to be identified (Luhrand Carmichael, 1980; Luhr et al., 2010; Crummy et al., 2014).

. This is an open access article under

Luhr and Carmichael (1980) proposed that the second half of thehistorical eruptive record of Volcán de Colima (the last 440 years) canbe characterized into cycles of activity. These cycles last around a centu-ry, and end with sub-Plinian to Plinian style eruption. Since the last‘end-cycle’ eruptions were in 1818 and in 1913, it is therefore impera-tive to a) contextualize the current activity at Volcán de Colima, andb) develop methods to help predict imminent end-cycle activity. Thefocus of this communication is to describe the activity around the 10thand 11th July 2015, which represents the most intense eruption since1913. We also try a non-routine method of petrologic characterization;

the CC BY license (http://creativecommons.org/licenses/by/4.0/).

101G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

using X-ray micro-computed-tomography (XMT), for rapid petrologicassessment of volcanic products has the potential to hold value(Pankhust et al., 2014). In our particular case we focus upon rapidlyestimating vesicle and crystal content.

2. Key context and real-time/near-real-time observations

2.1. Activity prior to the July events

In January 2013 Volcán de Colima showed signs of reactivation afternearly one and a half years in repose. A series of vulcanian explosionsformed a small crater on the lava dome which had formed between2007 and 2011 (Zobin et al., 2015). The explosionswere followed by ef-fusive activity. A new dome formed and rapidly filled the crater,overflowing towards the W, generating short lava flows.

BetweenMarch and October 2013 the flow rate was calculated to be0.1 to 0.2 m3/s. From October 2013 onwards, effusive activity was ac-companied by minor explosive activity. This activity diminished untilMay and July 2014, when it increased suddenly, reaching a maximumof 1–2 m3/s in September 2014 and fed twomain lava flows headed to-wards the W and SW.

At this time, explosions were stronger when compared with thosepre-July 2014. In particular, the explosionwhich occurred on November21st generated block and ash flows towards the S, SW and W flanks,reaching lengths of up to 2.5 km. The SW lava flow had reached a lengthof over 2.3 km by the 4th of January 2015, with a volume of

Fig. 1. A) RSEM. Daily number of events detected by automatic recognition based on Hidden ME) Sulfur dioxide measured with COSPEC starting on July 12th. ‘D = Dome extrusion’, ‘E = mo

11.7 × 106 m3, while the W lava flow had reached a length of 1.5 kmand a volume of ~5.8 × 106 m3.

Explosive activity was particularly notable on the 3rd of January2015, when an explosion occurred which generated 2 km long blockand ash flows to theN flank. The summit domewas gradually destroyedby the explosions, creating ~35 m deep oval-shaped crater with longaxis of ~200 m. Explosive activity subsequently decreased, yet the lavaflows remained active until February.

Beginning in May 2015, a new dome was emplaced, and it coveredthe entire crater floor with an irregular rocky surface formed by lavablocks (cf. the usual steep-sided nature of previous domes). Small ex-plosions were focused within the NE sector of the crater. During thenight of 2nd July a moderate-large explosion occurred. The numberand magnitude of explosions diminished significantly between the 3rdand the 7th of July (Fig. 1C).

Rockfalls started on the 3rd, and on the 7th of July two new lavaflows were observed heading towards the N and SW, with lengths of~620 and ~250 m respectively. Their emplacement was accompaniedby frequent rockfalls that produced small block and ash flows. The esti-mated lava flow volume was 3.9 × 106 m3.

The decrease in LP events in early July is real (Fig. 1D), and not theresult of filtering out seismic signals of rockfalls and/or PDCs (note theoffset by a fewdays before the substantial increase in rockfalls and PDCs).

Between the 8th and 9th of July a marked increase in the number ofrockfalls (Fig. 1B) was observed. These correlated in time with a periodof significant fumarolic activity visually observed near the summit dur-ing routine overflights, mostly on the S and E flanks. These observations

arkov Models (HMMs, Benitez et al., 2009), B) rockfalls and PDCs, C) explosions, D) LPs,derate explosion’, ‘C = Lava dome collapse’.

Fig. 3. Accretionary lapilli of the July 10th ashfall as observed in La Yerbabuena village at8 km from volcano.

102 G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

are consistent with a further increase in the extrusion rate. At 11:16 h(Local time= UTM− 6 h) on the 9th, a vulcanian explosion generateda 7 km high (a.s.l.) ash column and small PDCs towards the S sector ofthe summit.

On the10th of July a new~200m long lavaflowwas observed on theS flank of the volcano The increased fumarolic activity prevented obser-vations of the summit dome. The rest of the daywas characterized by anincrease in the number andmagnitude of rockfall events and associatedPDCs, which reached up to 2.5 km from the vent. Until this moment, theoverall behavior of Volcán de Colima was very similar to historical andrecent lava domes and associated lava flow activity.

2.2. The PDCs of July 2015

2.2.1. The first eventAt 20:16 h on the 10th July, a partial collapse of the dome occurred,

which generated a series of much larger PDCs. These PDCs were mostlychannelized by the Montegrande ravine on the S flank of the volcanowhere they reached 9.1 km in length (Fig. 2). The primary episodelasted 52 min (as illustrated by the seismic signal from the closest seis-mic station to the Montegrande ravine). A few PDCs were observed inthe San Antonio ravine.

An ash cloud generated from the PDCs traveled W–NW to distancesof up to ~150 km. Visual observations and seismic signal of this eventshow clearly that no eruptive column was associated with this process.Due to the strong winds and wet weather during the emplacement ofthe PDCs theW slopes were coated with ash, leaving the eastern slopesmostly ash free. The ash fall was in the form of accretionary lapilli (Fig.3). In Zapotitlán de Vadillo, 21 km NW of the crater, ash was observed

Fig. 2. Satellite image of Volcán de Colima and immediate surrounds, showing the dis

accumulated on vertical surfaces, another result of the prevailing hu-midity while the ash was falling.

The deposits were reconnoitered during an overflight the followingmorning. In some areas, small clustered circular crater-like structureswere observed, which are described as secondary depositional process-es in Stinton et al. (2014). Using the length and average cross-sectiondimensions of the ravine, we estimated a PDC deposit volume of2.4 × 106 m3, with a ±10% of error (240,000 m3).

tribution of the July 2015 PDCs along the Montegrande and San Antonio ravines.

103G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

2.2.2. The second eventAt 11:58 h on the 11th, nearly 16 h after thefirst series of PDCs a sec-

ond and considerably larger event commencedwith similar characteris-tics. This lasted for 1 h and 47min, and produced a series of PDCs whichwere emplaced along the same Montegrande ravine (Fig. 2). This eventalso did not produce an eruptive column (Fig. 4).

The deposit has a total length of 10.3 km, and reached a positionwhere the ravine opens to a fan-shaped valley (Fig. 5, see also Fig. 2).This flow crossed the power lines of Comisión Federal de Electricidad(CFE), stopping ~370 m beyond and to a position 6 km from Quesería(Fig. 2), the nearest large town within this drainage. In the head of theMontegrande ravine the PDCs overtopped the divide with the SanAntonio ravine, and advanced 2 km towards the La Joya and El Jabalíranches, which are located ~6 km away from the crater (Fig. 2).

Ash generated by this event traveled in two directions at different al-titudes. One plume traveled WNW (the typical wind direction) at highaltitudes (N2.5 km a.s.l.), which reached similar long distances as theprevious day's ash cloud. Ash was also dispersed to the S–SW by lowlevel winds, and produced ashfall in the La Yerbabuena and La Becerreravillages (which evacuated voluntarily) located 8 and 12 km SW fromthe vent (Fig. 2), which accumulated a 0.5 cm ash deposit. Ashfall wasalso observed in the cities of Colima and Villa de Álvarez (32 km fromthe volcano).

The total volume calculated for the PDCs of the second event was8.0 × 106m3. Including the ashfall, the first and second events produceda total of ~14.2 × 106 m3 of fragmentary material with ±10% of error(1,420,000 m3). Volumetrically minor PDCs were observed on the12th, but had essentially stopped by the 13th.

2.3. Description of the deposits and their impact

In the days after these events deposits and areas affected were visu-ally inspected. Field observations consistently demonstrated that whilethe dense portion of the PDCs remained channelized by the deep (~7–15m)Montegrande ravine, whenever there is a change of ravine direc-tion a dilute ash cloud surge decoupled from its PDC. The surge depositsare ~1–2 m thick at distances of up to 5 km from the vent. Decoupled

Fig. 4. Photograph of the second PDCs on July 11th, the absence of an

ash continued in the direction of the preceding PDC path, traveled hun-dreds of meters farther down slope, and invaded the wooded slopes todistances of a few hundred meters.

The decoupled ash produced a large halo of thermal impact upon theforest, from total carbonization to slight discoloration. The second eventblasted many trees which were incorporated into the flow andtransported downhill to the flow front. Many trees along theMontegrande ravine margins were burnt. During later fieldwork itwas noted that even after a month since deposition (about 2 m thick),the pyroclastic flow at the sample site was hot enough to combustpine resin upon tree trunks.

The deposits are poorly sorted, and all clasts are embedded in – andsupported by – a mixed matrix of sand and ash sized particles. Carefulrock-counting across the surface of the deposit from the second eventreveals it to be comprised of 20–30% scoria clasts (from cm to N1 m indiameter). Scoria is atypical of material deposits of explosions at Volcánde Colima, and as suchwe consider its presence in such abundance to behighly significant. A representative sample of this juvenile scoria (sam-ple VF-15-06) was collected on the afternoon of the 11th near the CFEpower lines.

The remainder of the non-scoraceous clasts are dense andesitelithics which frequently display bread-crust textures. These lithics canreach size of N3 m width and this maximum size is present at the finalfront, 10.3 km from the vent. Their composition and texture is consis-tent with derivation from lava dome destruction, and are much moretypical of fragmentary material from lava dome collapses during thepast few decades.

2.4. Post-event observations of summit activity

During overflights of the volcano from the 13th July onwards, anumber of post-event observations were made in the summit region.The scar left by the partial collapse of the summit dome and parts ofthe old crater wall were observed, shaped like an amphitheater(~100 m wide, ~180 m long and ~40 m high, for a calculated missingvolume of nearly 7.2 × 105 m3). The scar affected the feeder areas of

eruptive column is clearly evident in this image. View from East.

Fig. 5. Aerial view, looking to the North, near the lower end of- and oblique to- Montegrande ravine. This photograph shows the new PDC deposits (center of image) in the context ofVolcán de Colima and infrastructure. The two unvegetated parallel lines on the lower right of the image are corridors for CFE power lines.

104 G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

the N and SW lava flows, while the lava flow to the S had been engulfedin the collapsed material.

A new lava flow had been emplaced, probably immediately after thecollapse, and was being channelized by the amphitheater of the cratertowards the S. This lava flow measured 2.1 km in length by July 20th,with an estimated volume of ~7.0 × 106 m3. We calculate that it musthave advanced at least 400 m/day and had a flow rate of 6 to 7 m3/s,similar to the 2004 lava flow (Varley et al., 2010). This flow advanceduntil the 25th of August, having reached a total length of 2740 m andan estimated volume of 23.5 × 106 m3 with ±10% of error(2,350,000 m3).

Moderate explosive activity continued to the 11th August. Thisformed a wider and deeper amphitheater on the summit of nearly~200m in width and nearly ~50m in depth. The open side of the crateris ~90 m wide (Fig. 6).

2.5. Significance of July 2015 events in remote sensing datasets

The RSEM ‘Real-time Seismic Energy Measurement’ value or RootMean Square (RMS explained in De la Cruz-Reyna and Reyes-Dávila

Fig. 6.Viewof the summit before (4th February left) and after (11thAugust 2015, right) of themfrom SE to NW.

(2001) as measured at the closest seismic station from crater, wascalculated daily from May until August (Fig. 1A). The July PDCs rep-resent the maximum obtained since January 2013, and are amongthe highest values since monitoring began at this volcano (1989). Itshould be noted that the number and energy of rockfalls and PDCsduring July 8th–12th dominate the seismic record. This noise ob-scures the automatic detection of LPs or explosions within this peri-od (Fig. 1C–D).

The Geostationary Operational Environment Satellite system (GOES,http://goes.higp.hawaii.edu/volcanoes.shtml) detected a continuoushot spot (pixel 1 km2) over the volcano between the 10th and the30th of July. It, showed a high temperature in the crater area. This isbest explained by the presence of the lava flowwhichwas active duringthis period.

COSPEC retuned measurements of ~5000 t/d SO2 starting on the12th of July in response to the atypical eruption (Fig. 1E). Althoughthis SO2 degassing rate is lower than the highest recordedmeasurementon this volcano (20,000 t/d in 1998; Taran et al., 2002), these measure-ments are still considered remarkably high for this volcano that featuresa background flux b100 t/d (Taran et al., 2002).

ain activity of 10th–11th July. The open sideof the crater is ~90m. In both cases, the view is

Fig. 7. Example of 3D X-ray microcomputed tomography data.

105G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

3. Implications of monitoring data

These large collapses and resulting PDCs represent a significant andsudden increase in intensity above background in all monitoringsystems. Importantly, these events are also a departure from thedome-building and explosions style of activity. Together this set of ob-servations appears to correlate with the Luhr and Carmichael (1990)model (wherein Volcán de Colima shows an apparent cyclicity of Plinianeruptions every 100 years), which by extension indicates that end-cycleactivity is likely to occur imminently, and could be considered to havecommenced with these events.

Independent datasets reflecting to intensivemagmatic processes, in-cluding extremely high degassing rate and scoraceous juvenilematerial,point to a change in conduit dynamics. Arguably the most hazardouschange would be a scenario of accelerated ascent rate, which may indi-cate an increase in eruptible magma mobilization. In order to investi-gate this possible causal factor further, we selected a representativesample of the juvenile scoria to analyze.

4. Context – and observations – of the juvenile scoria

Juvenile magma of the Sub-Plinian–Plinian 1913 eruption containedsignificant amounts of stable (no breakdown reaction rims) hornblende(with a model proportion of ~3.7%; Luhr and Carmichael, 1990). Vola-tiles are compatible in its structure, thus if hbl is in equilibrium withthe host magma, in most cases the melt must contain N4.3 wt.% water(Rutherford and Hill, 1993; Moore and Carmichael, 1998; Carmichael,2002). High magmatic water and its potential influence on magmaexplosivity is argued to be an important factor that explains the 1913activity (Luhr, 2002; Savov et al., 2008).

The representative scoria sample (VF-15-06) from the second eventpreserves a several-cm wide banded texture of alternating pale-gray anddark-gray-matrixmaterial. This is in contrast with typical lava-domemate-rial which is dense, uniform in texture and color, and consistentlyinterpreted as magma that had arrived in the upper conduit in a degassedstate (e.g. Savov et al., 2008). Therefore this scoria sample represents thebest opportunity to infer magmatic processes unrelated to dome-building.

Accordingly, there is reason to pay special attention to the presenceand textural characteristics of hbl as indication of pre-eruptive magmawater content. Scoria from the second event was observed in the fieldto contain significant phenocrysts of hbl. Should abundant and stablehbl be observed (i.e. euhedral grains in clear contactwith glass or ground-mass), this would substantiate an argument for the eruption of wetmagma. It is important to note however, that the absence of hbl (or unsta-ble hbl) does not substantiate a strong argument against wet magma.

VF-15-06 contains plag N opx N cpx N oxides N hbl (see Table 1) withcrystal sizes from 5 mm to microlite set within banded matrix ofdevitrified groundmass. Mineral modes (see Table 1) were calculatedusing image analysis of a whole thin-section and individual major

Table 1VF-15-06 porosity and mineral modes using EDS image analysis, compared with other point-cmated at b0.01% (i.e. b10% absolute for hbl). Grains b30 μm2 are not considered in bubble-free

% mode July 2015 VF-15-06 1999 (n = 4) 1991 (n = 8)

Porosity 39.1Plagioclase 27.7 28.2 28.5Clinopyroxene 2.8 4.6 4.9Orthopyroxene 6.6 7.3 6.9Hornblende 0.2 n/o 0.6Fe/Ti-oxides 0.6 1.0 1.5Olivine n/o n/o 0.2Matrix 62.1 57.6 58.4Total crystals 37.9 41.1 42.6Cpx:Opx ratio 1:2.4 1:1.6 1:1.4Total (bubble free) 100.0 98.7 100.9

1991 and 1999 values are averages of those reported in Luhr (2002). 1982–1913 values from L

element maps (~55million pixels). Thesemapswere generated by rou-tine energy dispersive spectroscopy (EDS) at the University of Leeds.

We found no textural evidence for the presence of fresh hbl. Howev-er, we did find textural evidence of two types of hbl breakdown reac-tion: narrow, fine grained and rim-only zones, and broad, pervasiveand coarser grained zones. These appear to correlate with macro-texture of the sample, where the pervasive breakdown is found withindark-gray bands, and narrow rim breakdown within light-gray bands.Further work outside the scope of this study is required to confirmthese observations before attaching significance further than to simplyconclude that hbl is not stable in the July event scoria.

X-ray micro-tomography (XMT) data (generated at the ManchesterX-ray Imaging Facility) provides a greater volume of sample to be ob-served with full three-dimensional context. This is a key advantagehere given the rarity of hbl. It is also advantageous due to the rapid scan-ning capability of modern XMT systemswhichwithin amatter of hours,revealed evidence for hbl reaction (Fig. 7).

5. Discussion and interpretation

The marked increase in rockfall events on the 8th and 9th of Julyconcomitant with elevated fumarolic activity preceded the strongest in-crease in effusion rate (dominated by the major events of the 10th and11th of July). Together with the available SO2 data this chronology sug-gests that high-level magmatic degassing, causing destabilization of thedome, was occurring immediately prior to the main PDCs. Consideredalongside independent observations such as the lack of eruption columnand the presence of fresh scoriawithin the PDC deposits, it is reasonableto link anomalous and transient bubble-rich magma to the physical be-havior of the event.

As such we contend that the simplest explanation is that the arrivalof a batch of comparatively bubble-rich magma triggered the initialdome collapse, and can point to physical behavior before and after

ounted samples of recent lavas and 1913 scoria. Uncertainty on VF-15-06 modes are esti-mineral modes and instead contribute to matrix.

1982 (n = 2) 1976 (n = 4) 1961–62 (n = 9) 1913 (n = 4)

34.8 34.3 35.2 17.85.6 3.8 3.5 3.44.8 4.4 4.5 2.90.3 1.4 0.7 3.70.9 1.3 1.7 0.7n/o 0.4 0.1 n/o53.5 55.4 54.4 71.746.1 45.6 45.6 28.41:0.9 1:1.2 1:1.3 1:0.999.6 101.0 100.1 100.2

uhr and Carmichael (1990) and Luhr et al. (2010). n/o = not observed.

106 G.A. Reyes-Dávila et al. / Journal of Volcanology and Geothermal Research 320 (2016) 100–106

the event for continuity. The physical role of volatiles in the July 2015events is in stark contrast to dome-building stages, including the prior~6 months of explosions and lava flows. Finally, the lava flow emplacedafter the collapses and PDCevents can be simply explained by continuedextrusion of the comparatively degassed portion of the same magma.

The PDCs are the largest volume since the 1913 eruption; their sizelikely played a role in the long distances reached. Importantly, the high-ly fluidized nature of the PDCs required to reach run-outs of N10 km,while carrying large clasts mobilized to the end of the PDC run-outsimply a significant and sustained load-carrying capacity. Large volumesof air were likely engulfed by – and contributed to – the PDC to achievethis capacity, which is a feature of boiling-over (Rader et al., 2015). Theinclusion of both scoria and denser blocks exhibiting bread crust tex-tures within an ash matrix bear the textural hallmarks of boiling-over(Sulpizio et al., 2014; Rader et al., 2015; Dufek et al., 2015). Entrainmentand heating of air leading to extensive elutriation helps explain thewidespread ash cloud surge, similar to that observed at Tungurahuavolcano in the 2006 events (Hall et al., 2013).

Does the juvenile component of the July event PDCs appear similar tothe 1913 magma?

Total porosity of the scoria sample is ~39%, which is in contrast to thatexhibited by typical dense lava-dome samples (Savov et al., 2008), andmore similar to the juvenile 1913 deposits. Total crystallinity is ~38%and is the lowest since 1913. However the assemblage appears most sim-ilar to that of lavas from the previous ~50 years of extrusion (see Table 1),albeitwith less cpx and Fe-oxides. Opx andplag abundances however, areboth significantly greater than opx and plag abundance within the 1913Sub-Plinian-juvenile material (Luhr and Carmichael, 1990).

While some mineralogical variability is observed across a decadaltimeframe, hbl is conspicuously low in abundance (~0.2%). This is anorder of magnitude less abundant than that of 1913 scoria (Luhr andCarmichael, 1990). Furthermore, we have not observed stable hbl inthis representative sample.

The simplest petrologic interpretation is that the scoria representsthe same magma as the lava-dome building material, and not magmasimilar to the 1913. Thedifferences in the volatile content and total crys-tallinity can be explained by the lava dome samples experiencing longerdegassing and accompanying crystallization (Savov et al., 2008).

These events may simply demonstrate an end-member example ofnormal variation within this phase of activity. Since we have not ob-served this intensity before, the scale of the PDCs were unexpectedand linked to end-cycle activity. We note, however, that comparisonsto material erupted in the lead-up to the 1913 end-cycle eruption isnot possible — there appears to be no preserved record, and as suchwe cannot rule out the possibility that this anomalous PDC itself mayrepresent lead-indication of end-cycle activity.

Petrologicwork reveals that the only parameters approaching similar-ity with 1913 magma is that of the scoraceous (bubble-rich) nature andtotal crystallinity. Both of these parameters strongly influence the physi-cal nature of magmawhich help explain the July events status as the lon-gest PDC at Volcán de Colima since 1913. Because themineral modes andratios are considerably differentwe cannot suggest a similar petrogenesis,and thus similarities are likely to be governed by upper conduit physicaldynamics as opposed to deep-seated magmatic processes.

6. Conclusions

We favor a boiling-over mechanism to explain the anomalous erup-tions of July 2015 at Volcán de Colima. Arrival of an undegassedmagmabatch in the upper conduit displaced the dome in two principal events.This magma continued to ascend and feed PDCs which impacted thesurrounding region on a scale not observed since the 1913 end-cycleeruption. To date there is no compelling evidence to support a mecha-nistic comparison between these events and the last end-cycle eruptionin 1913. Further work is required to ascertain whether these events sig-nify an anomalous magma batch during a period of dome-building, a

change in upper conduit dynamics, or a fundamental switch in plumb-ing system regime that may lead to end-cycle activity.

Acknowledgments

We appreciate the support provided byUnidad Estatal de ProtecciónCivil del Estado de Colima, Unidad Estatal de Protección Civil del Estadode Jalisco, Coordinación Nacional de Protección Civil and Policía Federal.MJP gratefully acknowledges the support of anAXAResearch FundPost-doctoral Fellowship. Richard Walshaw, Lesley Neve and Sara Nonni arethanked for analytical assistance.

This work was made possible by the facilities and support provid-ed by the Research Complex at Harwell, funded in part by the EPSRC(EP/I02249X/1).

References

Benitez, M.C., Lesage, P., Cortés, G., Segura, J.C., Ibáñez, J.M., De la Torre, A., 2009. Automat-ic recognition of volcanic–seismic events based on Continuous Hidden MarkovModels. In: Bean, C.J., Braiden, A.K., Lokmer, I., Martini, F., O′Brien, G.S. (Eds.), TheVOLUME Project, VOLcanoes: Understanding Subsurface Mass MoveMEnt,pp. 130–139.

Carmichael, I.S.E., 2002. The andesite aqueduct: perspectives on the evolution of interme-diate magmatism in west-central (105–99°W) Mexico. Contrib. Mineral. Petrol. 143,641–663.

Crummy, J., Savov, I.P., Navarro-Ochoa, C., Morgan, D., Wilson, M., 2014. High-K maficPlinian eruptions of Volcán de Colima, México. J. Petrology 55 (10), 1–18.

De la Cruz-Reyna, S., Reyes-Dávila, G.A., 2001. A model to describe precursory materialfailure phenomena: application to short-term forecasting at Colima volcano,Mexico. Bull. Volcanol. 63, 297–308.

Dufek, J., Esposti Ongaro, T., Roche, O., 2015. Pyroclastic density currents: processes andmodels. Chapter 35. In: Sigurdsson, H., Loughton, B., McNutt, S., Rymer, H., Stix, J.(Eds.), Part IV Explosive Volcanism, The Encyclopedia of Volcanoes, second ed.,p. 620 (2015).

Hall, M.L., Steele, A.L., Mothes, P.A., Ruiz, M.C., 2013. Pyroclastic density currents (PDC) ofthe 16–17 August 2006 eruptions of Tungurahua volcano, Ecuador: geophysical reg-istry and characteristics. J. Volcanol. Geotherm. Res. 265, 78–93 (2013).

Luhr, J.F., 2002. Petrology and geochemistry of the 1991 and 1998–1999 lava flows fromVolcán de Colima, México: implications for the end of the current eruptive cycle.J. Volcanol. Geotherm. Res. 117 (1–2), 169–194.

Luhr, J.F., Carmichael, I.S.E., 1980. The Colima Volcanic Complex, México: part I. Post cal-dera andesites from Volcán Colima. Contrib. Mineral. Petrol. 71, 343–372.

Luhr, J.F., Carmichael, I.S.E., 1990. Petrological monitoring of cyclical eruptive activity atVolcán de Colima, Mexico. J. Volcanol. Geotherm. Res. 42 (3), 235–260.

Luhr, J.F., Navarro-Ochoa, C., Savov, I.P., 2010. Tephrochronology, petrology and geochem-istry of Late-Holocene pyroclast deposits from Volcán de Colima, Mexico. J. Volcanol.Geotherm. Res. 197, 1–32.

Moore, G.M., Carmichael, I.S.E., 1998. The hydrous phase equilibria (to 3 kbar) of an an-desite and basaltic andesite from western Mexico: constraints on water contentand conditions of phenocryst growth. Contrib. Mineral. Petrol. 130, 304–319.

Pankhust, M.J., Dobson, K.J., Morgan, D.J., Loughlin, S.C., Thordarson, Th., Lee, P.D., Courtois,L., 2014. Monitoring the magmas fuelling volcanic eruptions in near-real-time usingX-ray micro-computed tomography. J. Petrol. 55 (3), 671–684.

Rader, E., Geist, D., Geissman, J., Dufek, J., Harpp, K., 2015. Hot clast and cold blast: thermalheterogeneity in boiling-over pyroclastic density currents. The Use of Paleomagne-tism and Rock Magnetism to Understand Volcanic ProcessesGeological Society Publi-cation 396. IAVCEI, pp. 67–87.

Rutherford, M.J., Hill, P.M., 1993. Magma ascent rates from amphibole breakdown: an ex-perimental study applied to the 1980–1986 Mount St. Helens eruptions. J. Geophys.Res. 98 (19), 667–19,685.

Savov, I.P., Luhr, J.F., Navarro-Ochoa, C., 2008. Petrology and geochemistry of lava and asherupted from Volcán Colima, Mexico, during 1998–2005. J. Volcanol. Geotherm. Res.174 (4), 241–256.

Stinton, A.J., Cole, P.D., Odbert, H.M., Christopher, T., Avard, G., Bernstein, M., 2014. Domegrowth and valley fill during Phase 5 (8 October 2009–11 February 2010) at theSoufrière Hill Volcano, Montserrat. In: Wadge, G., Robertson, R.E.A., Voight, B.(Eds.), The Eruption of Soufriere Hills Volcano, Montserrat from 2000 to 2010. Geo-logical Society, London, Memoirs 39, pp. 113–131.

Sulpizio, R., Dellino, P., Doronzo, D.M., Sarocchi, D., 2014. Pyroclastic density currents:state of the art and perspectives. J. Volcanol. Geotherm. Res. 283, 36–65.

Taran, Y., Gavilanes-Ruiz, J.C., Corte.s, A., 2002. Chemical and isotopic composition of fu-marolic gases and the SO2 flux from Volcán de Colima, México, between 1994 and1998 eruptions. J. Volcanol. Geotherm. Res. 117, 105–119.

Varley, N., Arámbula-Mendoza, R., Reyes-Dávila, G., Stevenson, J., Harwood, R., 2010.Long-period seismicity during magmamovement at Volcán de Colima. Bull. Volcanol.72, 1093–1107.

Zobin, V.M., Arámbula, R., Bretón, M., Reyes, G., Plascencia, I., Navarro, C., Téllez, A.,Campos, A., González, M., León, Z., Martínez, A., Ramírez, C., 2015. Dynamics of theJanuary 2013–June 2014 explosive–effusive episode in the eruption of Volcán de Co-lima, México: insights from seismic and video monitoring. Bull. Volcanol. 77, 1–13.